Duplex transmission system



Feb. '21, 1928.

J. F. FARRlNGTON v DUPLEX TRANSMISSION SYSTEM Filed Dec. 24. 1920 dobn ff Farmhgfon. by

Patented Feb. 21, 1928.

tiNITED STATES PATENT orrics JOHN F. FARRINGTON, OF NEW YORK, N. Y., ASSIGNOR I O WESTERN ELECTRIC COM- PANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NE?! YORK.

DUPLEX TRANSMISSION SYSTEM. I

Application filed December 24, 1920. Serial No.432.9 )0.

This invention relates to duplex transmitting methods and systems and more particularlyto methods of and apparatus for duplex radio transmission for simultaneous telephony and telegraphy.

An object of the invention is toprovide a plurality of simultaneous signal transmission channels with a single carrier oscillation source. 5

Another object is to provide means Whereby an operator at a called radio station may break in on the operator at the calling station.

A feature of the invention is the provision of a duplex high frequency signaling system serving for simultaneous'telegraphy and telephony and having means for stepping down the received high frequency Waves to an intermediate inaudible frequency. enables greater amplification and selectivity to be had.

An additional feature of the invention is the provision of means for discriminating between and selectively indicating amplitude modulations of a carrier Wave such as are produced in ordinary carrier Wave telephony and prolonged constant frequency, changesin the carrier frequency itself such as may be used to transmit code signals.

Further objects of the invention Will be apparent upon consideration of the detailed description and claims. t

According to this invention a signaling station is provided With a source of oscillations which serve the double function of carrier Waves for anoutgoing transmission and reinforcing or intermediate frequency producing oscillations for the received Waves of an incoming transmission. The 'outgo ing carrier Waves may be modulated in any desired manner for one transmission. The frequency of the outgoing carrier Waves may be varied in accordance With a code for a second transmission. The two transmissions may therefore be simultaneous. At the dis tant station the 'modulatedwvaves of the first transmission are combined with locally generated reinforcingocillations to produce inaudible intermediate frequency modulated os-, cillatlons Which may be selected and detected.

The changed frequency carrier Waves are con'ibiued at the distant stationwith the locally generated reinforcing oscillatlonsto )lOClllCQ changed intermediate freouenc es. 1 .l

cillations. The changed intermediate fre- This includes a loop 4 antiresonant at the frecally generatedoscillations to give in a sec ond receiving circuit a beat note. vThetWo stations whichcommunicate with each other are similarly equipped the principal difference being due to the fact that their principal carrier oscillation sources generate oscillations which differ in frequency by the normal intermediatefrequency. A

In the draWing, Fig. 1 illustrates a duplex radio transmitting and receiving station equipped for simultaneous telephony. and telegraphy; F ig. 2 a similar system having a modifiedmodulator andFig. 3 illustrates a modification in-certain details of there ceiver at the right of line a-a in Figs. and 2. r

Referring to Fig. 1, a constant current modulating system 1, having an oscillator of Well known type, comprising three-element tube 2 and its associated circuits, is shown arranged for radio telephone transmission. (See Fig; 16 page 360 Free; A. I.-' E. E. March 1919.) The antenna is broadly tuned to the frequency 7", of the oscillations produced by source 2 and therefore serves to transmit oscillations of frequencies f +s and 7, representing respectively the side bands andv the unmodulated carrier component of speech modulated outgoing carrier Waves. The frequency of the speech Waves at this station is represented by 8 In order to change the carrier frequency f for code signaling, a key 6 is provided to short circuita reactance in the frequency determiningcircuit of the oscillator. For explanation purposes the reactance is of such character thatclosing the key 6 will decrease the carrier frequency. The distant communicating station, not shown, has similar transmitting apparatus except that its oscillator produces'Waves of frequency f and accordingly transmits to the station of Fig. 1, oscillations of frequencies f is and f representing,- respectively, the modulated side bands and 'unmodulated carrier frequency component, 8 denoting the frequency of speech Waves. to be transmitted from the distant station. In. order to .efiiciently select and receive the incoming Waves, the antenna of Fig. lis provided'with an additional path 3 tuned in conjunction with the transmitting antenna circuit to the mean frequency ofthe received Waves. This path which is determined by the amount of change tions of .nated by filter FL Which suppresses currents frequency 8 T1 ingly supplies transmission this inaudible difference or intermediate frequency component is modulated by Waves offrequency 8 and during incoming speech transmission by Waves of as Will be apparent by considering the frequencies of A loop 5 or appropriate-band filter adjusted to the normal intermediate frequencyf -"f but capable of transmitting the speech modulated intermediate frequency side bandsanda similarly selective coupled input -cir cuit of detector D selects the intermediate frequency-component for detection by dctector D to give in the associated receiver currents of speech frequency 8 or 8 as the case may be. A loop 7 and a. coupled input circuit of a. detector D are both tuned-to the changed intermediate When the operator at the distant station closes his key 6 to change the frequency of his outgoing carrier oscillations. Coupled to the input circuit of detector D is a. source G of oscillations of the'normal intermediate frequency f -f The detector D accord.-

to receiver With, a'Wave of the difference frequency of the normal and changed intermediate freuency-Waves. This Wave,'the frequency of in the carrier frequency f is preferablybelow the essential speech frequency range. 1L

filter FL may therefore pass this Wave and extinguish speech currents offrequencies s and s transmitted thru or produced at detector D The change in incoming carrier frequency and consequently in the intermediate frequency Will not seriously affect transmission of thespeech modulated Waves to detector D Telephony is therefore independent of telegraphy. Since the normal intermediate frequency oscillations produce no continuous low frequency beat note with oscillations from the source G, and the low pass filter excludes Waves of all higher frequencies than this note, the receiver R will normally give no response. The tendency to transmit speech currents to receiver R as a consequence of the combination at detector D of speech modulatedintermediate fre quency o cillations and reinforcing 0scillathe intermediate frequency, is elimiof the essential speech frequencies. The

operation at both stations is the same, due regard being had for the difference in the northe Waves combined.

frequency obtained:

R associated therethe same extent that the transmitting station'o'peratorchanges his own carrier Wave frequency for transmissionof telegraph signals. There Wlll accordingly be no beat note When the transmitting, operator closes his key but the note Will reappear when he opens it. Thisnotifies him that the receiving operator is trying to break in.

In Fig. 2 the oscillator and its associated key 6 are related as-in Fig. 1. The oscillator'instead of supplying modulated loscil-.

lations to an antenna isconnected to supply unmodulated oscillations to' an arrangement of tWo thermionic amplifiers in tandem. The second of these amplifiers, HA, transmits the amplified oscillations to the antenna and is provided, together with a speech controlled modulating tube M, With a constant space current source,.to enable modulation of theoscillations by amplifier HA. This constant current source consists merely of the ordinaryspace current source in series with a large speech frequency retard or choke coil. The operation of this modulating arrangement is identical in principle with that of Fig. 1, except that modulation takesplace at amplifier HA instea of at the oscillator.

In a system of the present typein which incoming and outgoing carrier Waves are combined, it is desirable that the carrier frequency shouldnot be changed during the process of modulation; thatis, the operation of the speech circuits in effecting modulalished'by the oscillator O Whichis not affected by impedance changes of the amplifier HA; in the process of modulation. .It is especially desirable that such rapid changes of carrierfrequency should notoccur in a system in which small carrier WZLVG frequency changes are employed to effect telegraphic communication as the undesired changes might be of the same order of'mag nitude'as the telegraphic changes and cause an interference. I

Consequently, the telephone communication may be regarded as occurring on a fixed lift) Wave length during periodsbetween telegraphic Wave length changes course, on the same invariable Wave length at all times When the telegraph portion of the system is not Working or between telegraph messages. The frequency changes referred to above are those Which occur With considerable rapidity during'the process of modulation (in some systems) and are entirely independentof the much more slowly occurring telegraph changes.

In the modification of Fig. '3, the generator G is designed to produce oscillations not of the normal intermediate frequency but differing therefrom by a frequency considerably exceedin the highest essential speech frequency asyfor example, by 5000 cycles. The frequency of oscillator Gr may there fore beeither f -f +5000 or f,'/ '5000. Detector D will yield in its output circuit oscillations of the difference frequency produced by'combining waves from source G and incoming changed intermediate frequency Waves representing telegraph signals. If the latter are of frequency f, f 15O), as it would be in'the case assumed, the output circuit of detector D Will yield Waves of frequency 5000i150 depending upon which of the tWo frequencies f f +5000 or -f '5000 is used for generator G. Band filter FE Will accordingly be designed to transmit Waves of either 4850 or 5150 cycles to detector D and to exclude currents of speech frequencies and of the 5000 cycle modulated and unmodulated currents which are produced by combination of normal intermediate" frequency speech modulated Waves and oscillations from. source G. The Waves transmitted by 'iilter FB are conibined'at detector l) With oscillations from asource G,, of frequency outside the transmission range of the filter, to produce an audible note preferably low in comparison With'essential speech frequencies. To the extentthat filter FIB does not'exclude speech modulated 5000 cycle currents, these Will give rise at detector D to speech currents and also to audible noise currents'resulting from the combination With oscillations from source G Filter FL designed to pass the lOW frequency audible telegraph note we cludes currents of the essential speech frequencies and substantially all of the noise current energy. I I

Should oscillations be'transmitted from generator G thru circuits 7 and 5 to detector 1),, these oscillations, if of normalintcri'nediate frequency, might combine at detector 13 With speech modulated changed intermediate frequency oscillations to give the difference frequency currents repre'sentnot speech, but speech currents modu- I lated by the'low frequency telegraph Wave and hence might produce an unintelligible llltllCfltlOn in the telephone receiver. If for and, of

example the incoming carrier wave frequency Were changed for telegraphy by150 cycles it Would'be represented by f 1 50 and the changed intermediate frequency ave as modulated by speech Would be represented by f f 150) is, which combined with the normal intermediate Wave of frequency f f Would result in the unintelligible Waves of frequencies 150+s and 15O--s...

frequencies and substantially extinguishes' currents of higher frequencies. 0

It should be understood that the invention is notto be limited to radio transmission nor to the systems, circuit details or sequence of operations disclosed but only by thescope of the appended claims. I

l/Vhat is claimed is: i

1(The method of high frequency signaling comprising transmitting and receiving a carrier Wave, producing an inaudible difference frequency Waveby combining With the received carrier Wave a second carrier Wave having another frequency, changing the carrierfrequency of said first'named carrier wave by an audible amount in accordance With signals and thereby producing a corresponding change in said difference frequency Wave, and producing from said difference frequency Wave an audible frequency Wave Whose frequency varies in accordance with the change in said difference frequency wave. c

2. The'method of high frequency signaling comprising transmitting and receiving a carrier Wave, producing a Wave of different frequency, combining said Waves to produce a beat frequency Wave, changing the frequency of said carrier Wave to transmit signals, and thereby producing a corresponding change in said beat frequency and producing with said beat frequency Wave a Wave Whose frequency equals said change. 3. In a system forcarrier Wave transmis- SlOIl in Which signals are transmitted by modulating a high frequency carrier Wave in accordance with modulation frequencv impulses and by changing the normal carrier frequency,- the method of reception Which comprises detectingthe modulation 1 component of the carrier Wave and detecting the changesin the normal carrier fr quency by causing a wave derived from the carrier Wave to continuously coact with a locally produced Wave to produce beats; i

4., In the method of simultaneous telephony'and telegraphy in which telephonic signals are transmitted as modulations of a carrier frequency Wave, and inwhichtelegraphic signals are transmitted by changing ill-3 ceived WfLVVWltll a locally produced wave,

the'frequency of which dilfers'from the nor mal carrier by an inaudible'amount, detect ing said combined waves, selecting from the detected wave the frequency component corresponding to the difference between the carrier and local frequencies, and stepping down said difference frequency to the value corresponding to the change in the carrierv frequency. q 7

5. The method of two-way signaling which comprisescontinuously transmitting in opposite directions between two communicating stationstwo high frequency waves differingv by an inaudible frequency, combining, at each station the received wave with a portion of the transmitted wave from the same station to give an auxiliary difference frequency wave, changing the frequency of the transmitted wave at either station by an audible amount in accordance with asignal, and detecting said signal at the other station by combining with the changed auxiliary frequency wave resulting from said signaling operation a wave having a frequency equal to the auxiliary frequency during non-signaling operation, and" separating from the product of the combining operation the audible frequency component which is present when signals are being distant station.

6. A method of simultaneous modulated carrier wave and high frequency signaling which comprises continuously transmitting from two communicating stations high frequency carrier 'waves differing from each other by an amount above good audibility, modulating either one of said waves in accordance with a low frequencyrwave simultaneously with the modulation changing the frequency of either of said carrier waves in accordance with a signal, combining at each station the normally received wave with'a portion of the transmitted, wave to give a modulated intermediate frequency carrier wave, detecting a portion of said intermediatevfrequency wave to reproduce the modulating wave, and combining with another portion of said intermediate frequency wave, a wave from a local source to give a result ant'audible beat note when either of the carrier frequencies is changed.

7. A carrier wave transmission systemineluding a source ofcarrier waves, means for changing the frequency of said waves to transmit low frequency impulses,a receiving station having a local source adapted to generate waves whose frequency differsat every instant fromthat of said-carrier Wave,

transmit-ted vfrom the.

detecting means responsive to the simultaneous action of said waves and the waves from said local sourceto produce a difference frequency wave whose frequency changesin proportionto'the change in fre quency of said carrier means for producing frequency wave a wave whose frequency equals said change.

8. In a transmission system including amodulated carrier wave channel and an additional high frequency wave transmission channel which utilizes the same carrier Wave,

meansfor changing the carrier frequency in order to transmit signals, and receiving.

means including alocal' source adapted to produce current whosefrequency di'ifers at' every instant by an inaudible amount jfromy frequency, means for combining: frequency from said carrier the carrier frequency and'the said source to "produce a difference frequency wave, and means for wave, and detecting. from said difference;

detecting the change of freque -cy' of said difference frequency: wave.

9. in av'carrier Wave transmissionsyst-em,

including transmitting and receiving circuits, means at and transmitting a modulated-carrier wave and at the latter, for detecting said Wave, additional means at the transmitter changing the carrier frequency by an audible amount, and circuit means at thereceiv-' ing circuit responsive to waves set upas the result of changes in said carrier frequency by said audible amount. r

10. A carrier wave transmission system comprising, in combination, means for gen crating and rier wave, means for changing the carrier frequency, a receiving conductor, a local receiver source generating a wavelwhich differs by an inaudible ainountfrom said carrier frequency, detectingvineans responsive to said carrier wave and thGWELVG fIQID said local source to produce a vdifference frequency wave, d-etecting'means for producing the modulating component from said 7 wave, and means for difference frequency I deriving from the difference frequency wave an audible frequency current when the trans-- mitted carrier frequency is changed.

11. A carrier wave transm ssionsystem comprising, in combination, means for gen-' erating and transmitting a. modulated car-j rier wave, means for changing-the carrier frequencyby an audible amount in accordance with a signal, areceivmgconductm',

the former for generatingfor,

transmitting a modulated car detecting means associated therewith, a'beat;

frequency detecting circuit also associated with said receiving conductor, said detecting circuit including means for giving afresulte ant beat note current having a, frequency equivalent to the change in said carrier frequency and including means for preventing" the beat frequency current from affecting said first mentioned detecting means. I

12. A carrier wave transmission system comprising, in combination, means for transmitting a modulated carrier wave, means for changing the carrier frequency, a receiving circuit, detecting means associated therewith, a local source also associated with said receiving conductor and adjusted to generate a current differing in frequency from" the normal carrier frequency by an inaudible amount, a combining device related to said local source and receiving circuit, means in the output circuit of said device selective to the difference frequency of said carrier and local source, a frequency changing means included in circuit with said selective means for decreasing said difference frequency to the value corresponding to the change in carrier frequency, and'an indicating means.

13. A two-way signal transmission system comprising two communicating stations each of which comprises, in combination, a source of high frequency waves, means forchanging said frequency, a transmitting circuit resonantto said frequency, a receiving circuit resonant to a frequency differing from said first mentioned frequency by an inaudible amount, means for combining a portion of the transmitted energy with energyreceived from the other station to produce an intermediate frequency wave, a second source of high frequencywaves related to said combining means, and additional means related to said'combining means and said second source and adapted to derive from the currents associated therewith, an audiblefrequency current during the intervals of changed carrier frequency.

14. A two-way'radio signal. transmission system comprising two communicating stations each of which comprises, in combination, a source of high frequency Waves,

means for changing said frequency by an audible amount, a transmittlng ClIClllt resonant to said frequency, a rece ving circuit resonant to a frequency differing from said first mentioned frequency by an inaudible amount, means for combining a portion of the transmitted energy with received energy to producean intermediate frequency wave, a second-wave source havinga frequency of generation equal to the normal intermediate frequency, combining means for the intermediate frequency waves and the Waves from said'second source, and means to-indicate the resultant difference frequency component when the frequency of the wave received from the other transmitting station is changed.

15. A two-way carrier wave transmisslon system comprising two stations each of which comprises, in combination, means for generating and transmitting a modulated carrier wave, meansfor changing the carrier frequefcy' by an audible amount in accord h signal, a receiving circuit res onant to a frequency differing by an inaudible amount from the transmitting frequency, detecting means for-combining a portion of the transmitted energy with the received energy to produce an auxiliary frequency modulated wave, a second detecting means associated with the output of said detecting means, a second source related to the output circuit of said first'mentioned detector, and additional means related to said output circuit and said second source for deriving from the currents associated therewith an audible beat note when the carrier frequency is changed at the distant station. q

16. A signaling system comprising an antennacircuit, a transmitting circuit connectedto said circuit, said antenna circuit being resonant at the frequency of waves to be transmitted, a circuit in shunt to said antenna circuit, reactance means in said shunt circuit for tuning saidantenna and shunt circuits together to resonance with the frequency of waves to be received, a receiver circuit coupled with said shunt circuit,re actance means in said shunt circuit whereby the impedance of said shunt circuit does not substantially affect the tuning of the system as'a whole for the transmitted frequency, said means permitting a relatively smallportion of energy ofthe transmitted frequency to be'received in said receiver circuit, and means for combining in said receiver circuit the energy of the normally received wave and said portion of the energy of the transmitted frequency which is received therein.

17. The method of radio signaling between two communicating stations, which consists in continuously transmitting a carrier wave from each station, varying the frein accordance with signals, beating thereceived wave at the other station with a portion of the wave normally transmitted from said other station'to produce a variable intermediate frequency wave, detecting said intermediate frequency wave to produce an audible frequency wave having signal frequency variations, and breaking-in on said signal transmisslon by simultaneously varylng the frequency of the wave transmitted from the other station.

18. The method of claim 17 in which the 'variationsin the carr er frequencies from the two stations are equal and in the same direction with respect to the normal frequency. v

j 19. The method of'two-way radio telephony and telegraphy between two stations which .consists in continuously transmitting a carrier frequency wave from each station, receiving sa d carrier wave at the other station, combining at each station a po tion of"thetransmitted wa ve with the i eceivedwave, 1:0 I produce intermediate quency of the carrier wave from one station 7 50' andsimpressing upon one of -wave,- means for varying the frequency of' the carrier wave from one station in accordance'with signals, means for beating the received wave at the other station with a portion ofthe wave normally transmitted from said other station to produce a variable intermediate frequency .wave, means for de- 2oitecting said intermediate frequency wave to :produce an audible frequency wave having signal frequency variations, and means' for breaking-in on said signal transmission by simultaneouslyVarying the frequency from said other station by the sameamount and 1 in the same direction as the variation at said transmitting station. n21. A twoway radio telephoneand telegraph system comprising means forcontinuso ously transmitting a carrier frequency wave from each of two communicating stations, -means for receiving said waves at the communicating stations, means for, combining at each station a portion of the normally transmitted wave with the normally received wave to produce an intermediate frequency wave, means for modulating the carrier wave .from one station in accordance with a voice signal wave, means for detecting the inter- .40 mediate frequencyiwave to reproduce the .voice si-gnal wave at the other station, means for simultaneously transmitting a telegraph signal overthe same carrier wave'used for voice. signalin and means whereby a receiving operator .can break in on said-telegraph transmission. 22. In a radio signaling station the combination of an aerial capacity and two branches connecting it'to earth, means for generating Waves of a frequency to be transmitted, means in the-other of said branches for rendering said other branch of higlrimpedanee to the .generated waves, means in one branch for tuning said aerial capacity to form a resonant combination for the impressed V waves, means in said-other branch for tuning said aerial capacity andasaid branches as a whole for currents of a frequency to be received whereby said branches andsaid aerial have a resonance peak at the frequency of waves to be received, and a receiving circuit coupled to said other branch including means for combining energy of said impressed and said branches received waves to produce combination frequency waves ofafrequency above good audibility.

23. A two-way radio terminal comprising elements for generating high frequency carthereby keeping said current constant, a signal controlled variable impedance device in shunt to said amplifier with respectto said source and means, and a transmitting conductor for transmitting the resultant variable amplified waves 1n combination with aneans for combining a-portion of the energ of the amplified waves with energy of a, signal modulated incoming'carrier waves to pro duce a new carrier wave, detecting means for the new carrier wave,.and ind cating :means for the resultant signal wave.

- 2a. The method of signaling which comprises producing carrier waves of substantially constant frequency, impressing the resultant waves upon the input circuit of an amplifier, supplying current of substantially constant value to the output circuit of said amplifier, variably diverting currentaway from said amplifier in accordance with signals to be transmitted, transmitting waveenergy of the resultant modulated waves,"combining a-portion of the resultant wave energy with received wave energy to produce aninaudible intermediate frequency carrier wave, and selecting and detecting the inaudible intermediate frequency carrier wave. I

25. A two-way signaling system comprising means for receiving and combining speech modulated energy .of an incoming carrier wave with energy of aspeech modulated outgoing-carrier, wave of another frequency in combination with a source of substantially constant frequency oscillations for producing the outgoing carrier wave, and an amplifier having its' anode circuit controlled by speech waves to modulate said oscillations. T

26; The method recited in claim 2 fv comprising the additional steps of simultaneously varying the frequency of said carrier waves in accordance with a second set sig vnals so that the resultant intermediate frequency'carrier wave has a corresponding frequency variation, and operating on said variable frequency intermediate frequency carrier. wave so as to independently obtain an audible frequency wave having signal fre-' quency variations corresponding to the second set of signals and to reproduce the first mentioned signals.

IHWVltIlQSS whereof, my, name this 22nd day I hereunto subscribe of December, A. D.,

JOHN rrraann srou. 

